On Thursday, 83-year-old Khieu Samphan and 88-year-old Nuon Chea were found guilty in a Phnom Penh court. A United Nations-backed tribunal had decided that these two men, elderly and frail as they are now, committed crimes against humanity more than 30 years ago. They were senior members of a regime that created the deaths of almost 2 million people.

With the sentences, the hope is that a horrific chapter in Cambodian history might be over. Finally, after almost a decade of investigation and a $200 million price tag, the Khmer Rouge's top leadership has been brought to justice. However, the severity of the crimes and the problems in bringing the perpetrators to trial mean many Cambodians will never forgive or forget.

The Khmer Rouge's name, and that of its main leader, Pol Pot, have become a short-hand for systematic cruelty and horror on an enormous scale. The reality is almost certainly impossible to imagine for people who were not there. Between 1975 and 1979, 1.7 million Cambodians are believed to have lost their lives. For a such a small country, that created an effect that lasts to this day: Almost one in five people living in Cambodia at the time is believed to have died as a result of Cambodian genocide.

Pol Pot, is seen June 22, 1979 in the Cambodian jungle. (AP Photo/Kyodo News)

Radicalized during a time of anti-imperialism and Communist ideology, Pol Pot (born Saloth Sar) and many other founders of the Khmer Rouge (officially the Communist Party of Kampuchea) were well-educated students who had lived in France yet felt alienated by post-independence Kingdom of Cambodia. In 1968, they formed the Khmer Rouge as an offshoot from the Vietnam People's Army from North Vietnam. The war in neighboring Vietnam helped shape Cambodian politics, and many historians now believe that a U.S. bombing campaign in their country drove many rural Cambodians into the arms of the radical ideology. On April 17, 1975, two years after the U.S. pulled out of Vietnam, Phnom Penh fell to Khmer Rouge troops and U.S.-supported government forces surrendered.

Just days after the Khmer Rouge took power, they ordered 2 million people living in Phnom Penh and other urban areas to head to the countryside. This was to be "Year Zero" in Cambodia's new rural, classless society, and the country would now be known as the Democratic Kampuchea. The idea was based on an extreme version of Maoism and a belief in the superiority of the Khmer people, the predominant ethnic group in Cambodia. Citizens were to be turned into traditional rural peasants, referred to as the "old people" by the Khmer Rouge. Urban workers and intelligentsia elites were viewed as "new people" and easily expendable. Survivors remember being told that the revolution would be successful without them: "To keep you is no benefit, to destroy you is no loss."

The move to the countryside was only factor in the changes. According to the Cambodian Tribunal Web site, "money, free markets, normal schooling, private property, foreign clothing styles, religious practices, and traditional Khmer culture" were all abolished. People were confined to their cooperative farms, and forced to wear traditional black outfits. Hundreds of thousands of soldiers, intellectuals, and minorities were imprisoned or killed. Of the 14,000 who entered one prison, a former high school renamed S-21, only seven were believed to have survived. As anti-Vietnamese paranoia set in, even Khmer Rouge loyalists found themselves executed.

A Cambodian man walks across a room filled with photos of dead prisoners in Tuol Sleng prison, also known as S-21 on August 7, 2014 in Phnom Penh, Cambodia. (Photo by Omar Havana/Getty Images)

The sites where people were killed and buried became known as the Cambodia's "killing fields." Those being killed were often hit over the head with clubs in a bid to save bullets. The Khmer Rouge's attempts to create a completely self-sufficient agrarian society led to thousands of deaths from starvation and overwork, and a lack of imported medicine led many others to die unnecessarily from diseases like malaria.

A Vietnamese invasion eventually forced the Khmer Rouge to give up its control of the central government in 1979. Most of the group's leadership went into hiding in Thailand and Western fringes of Cambodia. The group even renounced Communism in a bid to gain foreign support (and as part of a government-in-exile, they were able to retain Cambodia's United Nations seat for years). Years of inconclusive fighting with the government wore down the group, however. Following a peace deal in 1991, and democratic elections in 1993, the monarchy was restored.

In the 1990s, after years of defections and infighting, the Khmer Rouge was a spent force. Pol Pot himself died in 1998, never truly explaining what motivated reign of terror. Nuon Chea had been his deputy, "Brother Number Two" to Pol's "Brother Number One." Khieu Samphan had been head of state for Democratic Kampuchea between 1976 and 1979. Both have denied responsibility for the crimes against humanity they were found guilty of, and both are said to be planning appeals. It is unclear if a final decision for charges of genocide will be reached.

The long, difficult path of the tribunal had already been a source of frustration to many in Cambodia, in no small part due to opposition from current Prime Minister Hun Sen, a former Khmer Rouge soldier himself. While the tribunal was first recommended in 1999, delays meant that the trial didn't begin until 2011. Of the four senior leaders at the start, only two remain: Former Foreign Minister Ieng Sary died in 2013, while Social Affairs Minister Ieng Thirith was deemed unfit for trial the year before. The court has only dealt with one other case so far, that of prison director Kaing Guek Eav, sentenced to life imprisonment in 2011, and thousands of former Khmer Rouge commanders are still free.

So while Thursday's verdicts seemed like a victory, many weren't quite sure how to feel about it. “The crimes are huge, and just sentencing them to life in jail is not fair,” 54-year-old Chea Sophon told the Associated Press. His own brother had died in during the Khmer Rouge era. “But what can I do? Even if they die many times over, it would not be enough.”